Marine propulsion steam turbine installations



May 8, 1962 A. w. DAVIS 3,033,002

MARINE PROPULSION STEAM TURBINE INSTALLATIONS Filed Nov. 4, 1958 Inventor ALLAN VV/LL/AM DAV/s Attorneys ite States This invention relates to marine propulsion steam turbine installations of the type in which associated turbines working at different steam pressure stages transmit propulsive power through double-reduction gearing including a large slow-speed propeller-driving gearwheel to which the turbine shafts are geared.

In such installations, especially where there is reheating of the steam passing from one ahead stage to another, it is customary to have three associated ahead steam turbinesviz. high-pressure, intermediate-pressure and low-pressure turbines-in orderto take full advantage of the available temperature range of the steam.

The object of this invention is to devise for an installation of the type described an arrangement of doublereduction gearing by virtue of which it will be practicable and economical to have only two ahead steam turbines, namely a high-pressure turbine and a low-pressure turbine, and by so doing reduce substantially the overall capital and operating costs of such an installation.

Therefore, the invention is a marine propulsion steam turbine installation of the type described comprising a high-pressure steam turbine, a low-pressure steam turbine designed to develop considerably more power than the high-pressure turbine, a steam reheater through which passes the steam exhausted by the high pressure turbine to the low pressure turbine, two high-speed primary pinions driven by the two turbines, respectively, three medium-speed gearwheels of which one meshes with the high-pressure-turbine primary pinion and the other two mesh with the low-pressure-turbine primary pinion at opposite sides of it, and three secondary pinions which are connected to the medium-speed gearwheels, respectively, and which all mesh with the large slow-speed gearwheel.

An example of the marine propulsion steam turbine installation is illustrated by the accompanying diagrammatic drawing, which is a plan of the installation.

In the example shown, the boiler and turbine installa tion comprises the following combination of components, namely: two steam boilers It) and 11, with superheaters A and 11A, respectively; a re-heater 12, the tubes 13 of which are shown located in the path of the combustion gases in their flow from the furnace of the boiler 11 to the atmosphere; a high-pressure ahead turbine 14, to which a high-pressure astern turbine 15 is directly connected; a low-pressure ahead turbine 18, to which a low-pressure astern turbine 17 is directly connected; highpressure steam piping 18 from the superheaters 10A and MA by way of stopvalves 19 and the ahead manoeuvering valve 20 to the high-pressure ahead turbine 14; lowpressure steam piping 21 from the high-pressure turbine 14 to the re-heater 12 and further piping 22 from the re-heater to the low-pressure turbine 16; high-pressure steam piping 23 from a stop-valve 24 on the valve 20 and the astern manoeuvering valve 25 to the high-pressure astern turbine 15; low-pressure steam piping 26 extending from the high-pressure astern turbine directly to the lowpressure astern turbine 17.

The double-reduction gearing consists of the following combinations of components, namely: high-speed primary pinions 30 and 31 respectively on the shafts 32 and 33 of the high-pressure and low-pressure turbines; a mediumatent speed gearwheel 34 geared to the pinion 30 and two medium-speed gearwheels 35 and 36 both geared to the other pinion 31; three secondary pinions 37, 38 and 39 which are connected to the gearwheels 34, 35 and 36, respectively; the large slow-speed gearwheel 40 on the propeller shaft 41 with which gearwheel all three secondary pinions 37, 38 and 39 mesh. The axes of the primary pinion 31 and the gearwheels 35, 36 geared to it are in the same plane or nearly in the same plane; that is to say, these two gearwheels mesh with the primary pinion at more or less diametrally opposite sides of it.

In such a two-turbine installation, it is an economic necessity that the high-pressure turbine shall rotate at a much higher speed than the low-pressure turbine; for instance, the speed ratio may be 5 to 3. Seeing that the teeth of the secondary pinions 37, 38 and 39 must all have the same linear speed, the gearing must be designed to take into account the different primary-pinion rotational speeds. Thus, in the example, the low-pressureturbine double-reduction gear pairs 31, 35 and 38, 40 or 31, 36 and 39, 40 have lower gear ratios than the corresponding high-pressure-turbine gear pairs 30, 34 and 37, 40.

The lower speed of the low-pressure-turbine primary pinion 31, in comparison with the other primary pinion 30, requires that the low-pressure turbine shall have proportionately more than twice the high-pressure-turbine power in order to give an approximation to equality in torque between each of the low-pressure-turbine secondary pinions 38 and 39 on the one hand and the corresponding high-pressure-turbine secondary pinion 37 on the other hand. For instance, the power ratio between the turbines may be about 2 to 5 in the case instanced where the speed ratio is 5 to 3.

This considerable difference in power between the turbines of a two-turbine installation is practicable only by reason of the virtually extended temperature range derived from the re-heat system. Moreover, the transmission of the relatively great torque from the lowpressure-turbine primary pinion 31 is practicable mainly by reason of the locked train arrangement derived from the opposed medium-speed gearwheels 35, 36 insofar that the total low-pressure-turbine torque is divided equally between them and the heavy radially outward thrusts against them by the teeth of the pinion 31 are balanced or nearly balanced.

From the preceding description it will be apparent that despite the considerable difference between the turbines in power and the substantial difference between them in speed, the various gearing components of the installation can be designed to avoid any serious inequality in the gear-tooth pressures transmitted to the large gearwheel 40 by the secondary pinion 37 driven from the relatively low-powered higher-speed high-pressure turbine and by each of the secondary pinions 38 and 39 driven from the relatively high-powered low-speed low-pressure turbine.

In an example of the installation, it is estimated that the following data will be obtained, the figures being rough approximations given by wayof illustration.

l 28% inches of mercury, vacuum.

e,0es,002

In the example, the difference in speed between the turbines is taken into account not only in the three primary gear pairs 36-64, 31%35 and 3i--36 but also in the secondary gear pairs 37-40, 384l and 39-4t that is to say, the secondary pinion 37 issmaller than each of the secondary pinions 38 and 3% and is rotated at a higher speed. Nevertheless, it is practicable to have three secondary pinions all of the same size, in which event the primary gear pairs are designed to take into account the whole of the difierence in speed between the turbines.

In the example, the steam re-heater 12 is incorporated in the structure of the boiler 11 and derives its heat from the combustion gases. Any other appropriate type of re-heater may be used. For instance, the re-heater may be arranged separate from the boiler structure, or partitioned from the flue-gas system and may derive it heat from high temperature steam, which may be led through by-pass piping from the superheater 11A of the boiler 11. Such piping might branch from a point near the outlet of the superheaterand return from the re-heater to a point near the superheater inlet.

I claim: I

l. A two turbine steam marine propulsion installation for driving a propeller shaft comprising, in combination: only two steam turbines, one of said turbines being a high-pressure turbine and the other of said turbines being a low-pressure turbine, said low-pressure turbine being adapted to receive exhaust steam from said high-pressure turbine, and said low-pressure turbine being further adapted to develop more output power than that developed by the high-speed turbine; a steam reheater arranged to receive exhaust steam from said high-pressure turbine to increase the temperature of said exhaust steam and from which the steam is introduced directly into said lowpressure turbine; the low-pressure turbine being adapted to produce at least twice as much output power as the high-pressure turbine; each of said turbines having a rotatable turbine shaft; speed reduction gear trains operatively associated with each 05 said turbine shafts to transmit rotational motion from the turbine shafts to said propeller shaft; the speed reduction gear train for the high-pressure turbine comprising a primary pinion mounted on said high-pressure turbine shaft, said primary pinion meshing with a first speed reduction gear, a secondary pinion driven by said first speed reduction gear for rotational movement in conjunction therewith, a second speed reduction gear mounted on said propeller shaft and meshing with said secondary pinion; the speed reduction train for the low-pressure turbine comprising a primary pinion mounted on said low-pressure turbine shaft, said primary pinion meshing with a pair of first speed reduction gears along substantially diametrical portions of said primary pinion, a secondary pinion driven by each of the said pair of first speed reduction gears for rotational movement in conjunction therewith and meshing with said second speed reduction gear mounted on the propeller shaft.

2. The steam turbine marine propulsion installation of claim 1, wherein the high-pressure turbine is adapted to rotate at a speed of rotation greater than the speed of rotation of the low-pressure turbine, the speed reduction gear train associated with the high-pressure turbine shaft being further adapted to provide an overall speed reduction ratio greater than the overall speed reduction ratio of the speed reduction gear train associated with the low-pressure turbine shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,274,320 Pavlides July 30, 1918 2,747,373 Eggenberger et a1 May 29, 1-956 FOREIGN PATENTS 666,333 Great Britain Feb. 3, 1952 

